AdWords Ad Descriptions

Historically capitalising each word provided a higher CTR. So did the word free, in any context, and so did an exclamation mark.

With ad extensions and more characters in general, things have changed. Ads are sometimes a chore to read now, and if you actually want people to read the description line, normal sentence capitalisation is working best. Same goes for call-outs and sitelinks.

However there's no one size fits all in this business...

So in your ad group with the most impressions, do a A/B test and see which works for your audience. A 10% improvement in CTR means roughly a 10% decrease in click costs, so it is always worth testing new ad copy.